The embodiment of the invention discloses an SIM (Subscriber Identity Module) card switching method and device. The method comprises the steps of obtaining network information of a mobile network in which a first SIM card is located, wherein the first SIM card is a master card; determining whether the first SIM card is switched from a first network with high transmission speed to a second network with low transmission speed or not according to the network information of the first SIM card; judging whether a third network of which transmission speed is higher than that of the second network exists in a neighbor cell of a second SIM card (namely an auxiliary card) or not; and switching the second SIM card to the third network of the neighbor cell if the third network exists in the neighbor cell of the second SIM card, starting the data traffic channel of the second SIM card, and moreover, closing the data traffic channel of the first SIM card. Data traffic can be switched between the different networks with the relatively high transmission speed, a user can operate under a high-speed network environment in as much as possible time, and the mobile network speed of the user is improved.